Cleanup Plot, cumulative -> histogram, smoothening
Cleanup Plot, cumulative -> histogram, smoothening

- Use Qt backend if we can display, since that works on the DAS after
  long installation.
- Moved most of the code into a class
- Remove the cumulative histogram code and replace it with a normal
  frequency histogram, with a binning parameter
- Draw a smoothened line of the frequencies. Split into negative and
  positive sections in order to not confuse the smoothening operation.
  Most of the smoothening/interpolation/spline operations on the web
  seem to not work well on our data, probably because of weird
  distribution of frequencies (classifier favors some fractions, etc.).
  Some more tuning might be necessary.

timvandermeij/sentiment-analysis,timvandermeij/sentiment-analysis